Nearly every modern building has some form of HVAC system for heating, ventilation, air conditioning, and moving air within the building. An efficient, effective HVAC system is necessary not only for the comfort of the occupants of a building; but, as has become increasingly clear relatively recently, for the mental and physical health of such occupants. Although there are many variations of HVAC systems, in general such systems include a variety of air ducts, at least one fan for moving air, a filter, a heating coil, a cooling coil, a method of recycling air within the system (return air or R/A), a method for introducing outside air into the system (outside air or O/A), and a method for expelling air from the system (exhaust air or E/A). The filter, heating coil, cooling coil, and fan are ordinarily located together in what will be referred to here as a treatment node. The treatment node is usually located in a spot within the HVAC system which is easily accessible. Treated air leaves the treatment node in a downstream direction and is transported through a series of ducts to various locations within the building. Air enters the treatment node from upstream.
Return air (R/A) ordinarily enters the treatment node from upstream after passing through a controlled R/A damper. Exhaust air (E/A) ordinarily exits the system upstream from the R/A damper through a controlled E/A damper. Any E/A is a portion of R/A removed upstream from the R/A damper. Outside air (O/A) enters the system upstream from the treatment node and downstream from the R/A damper through a controlled O/A damper. R/A and O/A mix prior to entering the treatment node. This mix of air, referred to as total air here, passes through the filter to remove particulate matter and then is either heated or cooled as necessary by passing through the heating coil or the cooling coil with either the heating or cooling coil activated. Typically, HVAC systems are either pull-through systems where the fan is at the downstream end of the treatment node and pulls air through the treatment node, or push-through systems in which the fan pushes air through the treatment node with elements such as the heating and cooling coils located downstream of the fan.
In a conventional commercial HVAC system, various sensors track various parameters including the static pressure, temperature, humidity, and carbon dioxide content of the air within the system. These parameters are used to control the various dampers which determine the volume of R/A, E/A, and O/A. If the carbon dioxide content becomes too high, for instance, there will be more O/A and also more E/A to decrease the carbon dioxide content. Many HVAC systems have additional fans such as an exhaust fan to aid in the removal of E/A. Many residential systems do not have E/A or O/A options within the HVAC system. Many HVAC systems include an air blender upstream of the filter to mix the R/A and O/A which improves heat transfer within the treatment node.
Although there are a variety of heating and cooling methods, there is nearly always a working fluid which passes through either the heating or cooling coil. Most often a boiler heats the liquid which then passes through the heating coil. When the heating coil is activated, heated water, which is significantly hotter than the air, heats the air passing through the heating coil which causes the temperature of the water to decrease and the temperature of the air to increase. The water is returned to the boiler where it is reheated. The effectiveness of the heat transfer of the heating coil can be determined with relative ease, because the total energy which the heating coil produces may be measured and the energy actually transferred to the air may be determined using the method of the instant invention. By comparing the total energy which could have been transferred if the heating coil were 100% efficient with the amount actually transferred, the efficiency of the heating coil in its current condition may be determined. As will be understood, the same method may be used to determine the efficiency of a cooling coil or other similar element. Although there are various heating and cooling systems incorporated in HVAC systems, the operating method and method of determining efficiency are very similar.
The efficiency of an HVAC system is affected by a great many factors. Poor maintenance of ducts and equipment greatly reduces efficiency. Clogged or dirty filters, heating coils, or cooling coils also greatly reduce the efficiency of an HVAC system. It is currently relatively easy to determine whether an HVAC system is operating, generally, more or less efficiently than it operated at a previous time. For example, if the boiler burned X gallons of fuel to heat the building for twenty-four hours last year when the outside temperature was twenty-six degrees and this year the boiler burns 1.5× gallons of fuel to heat the building at the same outside temperature, the efficiency of the systems has been greatly reduced. However, it is believed to be nearly impossible at the current time to determine the operating efficiency of the various elements of an HVAC system, including filter, heating coil, and cooling coil separately with any accuracy. For example, it is not currently possible to accurately measure the effect of changing the filter or filters. The same applies, for instance, to cleaning the heating or cooling coil. At the current time it is even relatively difficult to determine the actual air flow within an HVAC system.
Using the current state of the art, it is very difficult to obtain correct measurements to either determine the efficiency of the elements of an HVAC system or even to determine the air flow through the system. The volumetric air flow through a conventional HVAC system is usually measured by measuring the velocity pressure just downstream of the treatment node using a pitot tube. Many measurements must be taken across a cross section of a duct such that a matrix of measurements are taken. Generally, the more measurements taken the more accurate this method of measuring becomes. This method is expensive and time consuming because a large number of measurements are required to be taken; and it is not particularly accurate because the air is ordinarily not thoroughly mixed at this point in the system and human error often becomes a factor.
Because of fuel costs and various other factors, conservation of energy is and, most likely, always will be extremely important. A significant portion of our total energy use is wasted by inefficient HVAC systems. If, for instance, the cooling coil in an HVAC system is not cleaned or replaced when it should be or is cleaned or replaced when it isn't necessary, energy or money is wasted. If an HVAC system is poorly designed or doesn't actually operate as well as it should considering the design parameters, energy is wasted.